Printed circuit boards have metallized pads or areas that are soldered to component leads or pads. Several methods of soldering are currently used, such as printing solder paste and reflowing the paste, placing solder preforms on the pads and then reflowing the preforms to solder the component in place, mass soldering (wave soldering) the components in place, or providing the solder on the board in reflowed form prior to placing the component. The latter method uses circuit boards that are referred to as "clad". That is, the component pads on the board have a pre-applied quantity of solder already reflowed in place. This process leaves each pad with a domed mass of solder on the pad. Components are then placed on the board, and sometimes they are temporarily held in place with a tacky material such as flux. When parts are placed on these domed structures, they tend to skid off the top of the dome, and become misaligned. This is because the rounded surface of the solder pad presents a non-planar surface for the part, creating an unstable situation. When the components sit on top of the domed structure, small forces exerted on the circuit board by assembly line conveyors or robots cause the part to slide off the pad. This vibration or mechanical bumping can dislodge the part, ultimately creating a defect in the soldered assembly. Such defects appear as shorts and/or unsoldered leads. Heavy or tall components with large mass or high center of gravity overcome the surface tension provided by the tacky flux, that works so well for small parts.
One method of solving this problem has been to mechanically flatten the domed bumps using rollers or heated platens. While this is a viable solution, it is not the most desirable, since it is a secondary operation and adds extra cost to the product.
It would be a desirable addition to the art if one could devise a way to hold the parts in place without the added expense incurred to flatten the domed surfaces of the solder pads.